Two material injection molding may comprise the injection molding of plastics materials having different characteristics so as to provide a composite product. Two material injection molding may, for example, allow an elastic plastic material to be molded onto a rigid plastic material to improve the feel or touch of the material, allow for absorption of shock and vibration and/or to provide sealing against dust, water and other agents. Other applications of two material injection molding technology includes plastic parts with moveable assemblies, living hinges, decorative features, combinations of transparent and non-transparent areas, different colours and the like.
In two material plastic injection molding technology currently available, commercially available injection molding machines are provided with a mold specifically built for the product. These molds commonly have two internal passages directing the two plastics materials injected by the molding machine to the two mold stations which have been constructed to correspond, or be complementary, to the geometry of the plastic part. Each of the two mold stations is made up of a group of inserts constructed of tool steel to the required geometry. Production of the plastic part involves injecting the first material into the first station and then transferring the partially completed plastic part to the second station where the second material is injected. With such conventional two material injection molding technology, change over of production from one product to another requires replacement of the entire mold and subsequent readjustment of the injection molding machine. Such a process typically takes about four to six hours to complete.
Thus conventional two material injection molding involves two major equipment items. Firstly an injection molding machine with the ability to inject two plastic materials sequentially into a mold, and secondly an injection mold comprising a mold framework and a non-changeable plastic insert made according to the geometry of the two material plastic product. The mold framework, which is commonly known as the mold base, used in such conventional two material injection molding, is essentially the same as those designed for a single material injection molding. The mold base may be mounted on a turntable device built as an integral part of the molding machine. Rotation of the turning device enables two different materials to be injected sequentially into the product inserts thus forming a two material plastic part. Rotation of the turntable thus is about an axis which is transverse to the axis of movement of the moving part of the mold framework.
The principal disadvantage of such constructions is the significant time, as stated above, which it takes to change the two material injection molding device from a first set up to mold a first product to a second set up to mold a second product.